It must, however, be remarked that the term substitution would be preferable to conversion. There is, at present, no evidence to show that the germinal vesicles were present in these cases; on the other hand, it seems most probable that they were not, so that the presence of the pollen-cells must be considered as simply adventitious. It can hardly be that they were, in the first instance, germinal vesicles, which, in course of time, became so modified as to assume the appearance of pollen-grains. Between the nucleus of the ovule and the tubercle of cellular tissue constituting the primordial anther, there is little or no difference, so that it may be said that, for a time, there is no distinction of sex in the nascent flower, but as development goes on, the difference becomes perceptible. It cannot at present be stated what precise circumstances induce the one mass to form mother-cells and pollen-grains, and the other to develop an embryo sac and germinal vesicles. Position and external circumstances may have some indirect effect, and it may, perhaps, be significant that in all the instances of polliniferous ovules, the ovular structures have been exposed on an open carpel or otherwise, in place of being confined within the cavity of a closed ovary, as under ordinary circumstances. Even among Conifers the ovuligerous scales are so closely packed that there is little or no exposure of the ovules. But, apart from all speculative notions as to the relation between the structure and functions of the anther and of the ovule respectively, and of the possibility or the reverse of parthenogenesis, it will clearly be necessary in any future alleged occurrence of the latter phenomenon to ascertain whether any or all of the apparent ovules are, or are not, anthers in disguise.
=Homomorphic flowers of "Compositæ."=--In a large section of the _Compositæ_ there is, as is well known, a distinction between the florets of the "disc" and those of the "ray," the latter being ligulate, the former tubular.
In what are erroneously called double flowers in this order, _e.g._ in the Chrysanthemum, Dahlia, &c. &c., the florets are all ligulate. This change is sometimes classed with peloria, but there is no abnormal regularity in these cases. On the other hand, were the ligulate florets to be all replaced by tubular ones, the term peloria would be more strictly applicable. It will be remembered that in the sub-order _Ligulifloræ_, the florets are naturally all ligulate, so that the change above mentioned is not in itself a very grave one.